In the context of traffic control, a lane is part of a carriageway (roadway) that is designated for use by a single line of vehicles, to control and guide drivers and reduce traffic conflicts.[1] Most public roads (highways) have at least two lanes, one for traffic in each direction, separated by lane markings. On multilane roadways and busier two-lane roads, lanes are designated with road surface markings. Major highways often have two multi-lane roadways separated by a median.

Some roads and bridges that carry very low volumes of traffic are less than 15 feet (4.6 m) wide, and are only a single lane wide. Vehicles travelling in opposite directions must slow or stop to pass each other. In rural areas, these are often called country lanes. In urban areas, alleys are often only one lane wide. Urban and suburban one lane roads are often designated for one-way traffic.

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Lane capacity varies widely due to conditions such as neighbouring lanes, lane width, elements next to the road, number of driveways, presence of parking, speed limits, number of heavy vehicles and so on - the range can be as low as 1000 passenger cars / hour to as high as 4800 passenger cars /hour but mostly falls between 1500 to 2400 passenger cars / hour.[2]

Transfer lanes, connecting surface collector lanes with through lanes between two tunnels

A left-turn merging lane in Germany, needing explanation by a crafted sign

A traffic lane or travel lane is a lane for the movement of vehicles traveling from one destination to another, not including shoulders.

A through lane or thru lane is a traffic lane for through traffic. At intersections, these may be indicated by arrows on the pavement pointing straight ahead.

An express lane of a road is used for faster moving traffic and has less access to exits/off ramps. In other areas, an express lane may refer to a HOV lane (see below).

A reversible lane (contraflow lane) is a lane where the direction of traffic can be changed to match the peak flow. They are used to accommodate periods of high traffic flow, especially rush hour where the flow is predominantly in one direction, on roads that cannot be easily widened such as over bridges. One or more lanes are removed from the opposing flow and added to the peak flow.

An auxiliary lane is a lane other than a through lane, used to separate entering, exiting or turning traffic from the through traffic.

An acceleration lane or merge lane allows traffic entering a highway to accelerate to the speed of through traffic before merging with it.

A deceleration lane is a lane adjacent to the primary road or street used to improve traffic safety by allowing drivers to pull out of the through lane and decelerate safely before turning off a surface street or exiting a freeway.

A turn lane is set aside for slowing down and making a turn, so as not to disrupt traffic. By removing turning traffic from the through lanes, motorist safety is improved and delay is removed, but crossing distances for pedestrians are lengthened, increasing their exposure to collisions.

A two-way center turn lane is a lane in the center of a roadway to allow drivers traveling in either direction to pause before turning across oncoming traffic (a left turn in right-driving countries, or a right turn in left-driving countries) while waiting for a gap in traffic.

A passing lane is sometimes provided on busy two-lane roads to allow drivers to pass slower vehicles without having to cross the center line and risking a head-on collision.

A climbing lane, truck lane, or crawler lane is often provided on steep mountain grades, in order to allow smaller vehicles to pass larger, slower ones. The lane is marked only on the uphill stretch and usually a short distance afterward (for regaining speed).

An operational lane or auxiliary lane is an extra lane on the entire length of highway between interchanges, giving drivers more time to merge in or out. The lane is created when an entrance ramp meets the highway, and drops out (with an "exit only" sign) to become the ramp at the next exit.[3]

A transfer lane of a road is used to move from express lanes to collector lanes, or vice versa; it is somewhat similar to an auxiliary lane.

A collector lane of a road is used for slower moving traffic and has more access to exits/off ramps.

Dedicated lanes are traffic lanes set aside for particular types of vehicles.

A high occupancy vehicle or carpool lane is reserved for carpooling. In the US, they may be marked with a diamond icon every few hundred feet (hence the nickname "diamond lane"), or separated from other lanes by double broken white lines, a continuous pair of double yellow lines, or just a single broken white line.

A designated bicycle lane is a portion of the roadway or shoulder designated for the exclusive or preferential use of bicyclists. This designation is indicated by special word and/or symbol markings on the pavement and "BIKE LANE" signs.

A motorcycle lane is provided at certain roads and highways such as the Federal Highway in Malaysia to segregate the motorcycle traffic from the main roadways to reduce motorcycle-related accidents. The motorcycle lane may form a part of the hard shoulder, or may be one or more completely separated lanes.

A bus lane is reserved for buses providing public transportation on a fixed route, sometimes with overhead catenary for trolleybuses. In some countries, bus lanes may also be used by some other traffic, such as taxis, bicycles and motorbikes.

A tram lane is a lane reserved for the use of buses, trams and taxicabs. It is usually encountered in cities with curbside tram network, such as Zagreb.

A truckway is a dedicated lane for longer length trucks; for instance, the Florida Turnpike allows 29.3 meter double trailer combinations, in contrast to normal Florida highways' 16.2 meter limit. Since the major cost of trucking is the fixed cost of the same trailer with its driver the cost per ton of operating with truckway size and weight allowances is 35 to 40 percent below the cost of operations on the non-truckways.[4]

In some areas, the lane adjacent to the curb is reserved for non-moving vehicles.

A loading lane (loading zone in the United States) is an area next to a curb, which is reserved for loading and unloading passengers and/or freight. It may be marked by a sign ("LOADING ONLY" or "LOADING ZONE") or by a yellow or white-painted curb.

A hard shoulder is sometimes called an emergency lane or a breakdown lane, when it is reserved for breakdowns, and for emergency vehicles. On some congested roads, the shoulder is used as a vehicle lane during peak travel hours.

By law or custom, inside lanes are often reserved for faster traffic, and outside lanes are used by slower traffic.

An overtaking lane is the lane furthest from the shoulder of a multi-lane carriageway/roadway (sometimes called the fast lane, although this is deprecated by the authorities).

The slow lane is the lane nearest to the shoulder of a multi-lane carriageway/roadway.

These usages lead to the phrases life in the slow lane and life in the fast lane, used to describe relaxed or busy lifestyles, respectively and used as the titles of various books and songs.

The widths of vehicle lanes typically vary from 9 to 15 feet (2.7 to 4.6 m). Lane widths are commonly narrower on low volume roads and wider on higher volume roads. The U.S. Interstate Highway System uses a 12-foot (3.7 m) standard for lane width, while narrower lanes are used on lower classification roads. In Europe, as laws and road width vary by country, the minimum widths of lanes is generally between 2.5 to 3.25 metres (8.2 to 10.7 ft).[5]

On higher speed rural roads, narrower lanes are likely to have more lane-departure crashes such as run-off-road collisions and head-on collisions. In urban and suburban areas, the effect of lane width on safety is much smaller.

A typical rural American freeway (Interstate 5 in the Central Valley of California). Notice the yellow line on the left, the dashed white line in the middle, and the solid white line on the right. There is also a "rumble strip" on the shoulder, not easily seen in this view.

Painted lane markings vary widely from country to country. In United States, Canada, Mexico, Honduras, Puerto Rico, Virgin Islands and Norway, yellow lines separate traffic going opposite directions and white separates lanes of traffic traveling the same direction, but such is not the case in many European countries.

Lane markings are mostly lines painted on the road by a road marking machine, which can adjust the marking widths according to the lane type.[8]

Traffic reports in California often refer to accidents being "in the number X lane." The California Department of Transportation (Caltrans) assigns the numbers from left to right.[9] The far left passing lane is the number 1 lane. The number of the slow lane (closest to freeway onramps/offramps) depends on the total number of lanes, and could be anywhere from 2 to 6.

For much of human history, roads did not need lane markings because most people walked or rode horses at relatively slow speeds. Another reason for not using lane markings is that they are expensive to maintain.

When automobiles, trucks, and buses came into widespread use during the first two decades of the 20th century, head-on collisions became more common.

Without the guidance provided by lane markings, drivers in the early days often erred in favor of keeping closer to the middle of the road, rather than risk going off-road into ditches or trees[citation needed]. This practice often left inadequate room for opposing traffic.

There are two people who have been credited with the invention of lane markings. In 1911, Edward N. Hines, the chairman of the Road Commission of Wayne County, Michigan was trying to make roads safer. He supposedly came up with the idea of painting stripes to separate lanes of traffic after riding behind a milk truck that leaked milk onto the center of the road, leaving a stripe.

June McCarroll, a physician in Indio, California started experimenting with painting lines on roads in 1917 after she was run off a highway by a truck driver. In November 1924, after years of lobbying by Dr. McCarroll and her allies, California officially adopted a policy of painting lines on its highways. A portion of Interstate 10 near Indio has been named the Dr. June McCarroll Memorial Freeway in her honor.

By 1939, lane markings had become so popular that they were officially standardized throughout the United States, and they were soon copied worldwide.